OK, there is possibly a clash with peer guardian and the web shield and removing one removed the clash. You could try terminating the web shield and enabling peer guardian, this should show if it is a clash between the two or if it is peer guardian (if it still doesn’t work) causing the problem.
avast isn’t a firewall (so you need one) and as such doesn’t block, the web shield just scans http traffic.
You could try this and see if it allows you to keep peer guardian enabled, but it means that the web shield won’t be monitoring that stream IP.
A way around it would be to add the IP address not domain name to the Web Shield, Customize, Basic tab, Ignored addresses: field, e.g. 123.123.123.123 you would obviously have to find out exactly what the IP address is.
Stick around and browse the forums, especially the sticky topics at the top of each of the forums, not to mention the avast file. They provide a wealth of information to help you get the best from avast.